THE INDIVIDUAL LIFE CYCLE 187 



fire of life is smothered in its own ashes. But why should 

 there not have been more perfect sifting ? It is said that 

 the regulative system — made up of the organs of interna 1 

 secretion — loses its activity. But why ? It seems as if 

 these were rather symptoms than causes of old age ; 

 we can conceive of ways in which they might be evaded. 

 There must be some more radical imperfection. That 

 is disclosed when we ask whether it is really the case that 

 all living creatures must and do grow old and die. The 

 answer is in the negative. Most of the simplest or- 

 ganisms are continually making good their wear and 

 tear, and seem to be exempt in natural conditions from 

 natural death. There is good reason to believe that 

 even some of the simple multicellular animals, like 

 fresh-water polyps and Planarian worms, are able to 

 stave off natural death indefinitely. Natural death is 

 due to a mounting up of physiological debts — part of 

 the bill is paid in every meal and in every night's rest, 

 but the book is never cleared and in spite of hohdays 

 which knock off big arrears there is always a growing 

 balance against us. Let us not press the metaphor too 

 far ; it is to ourselves we are in debt. Now the very 

 interesting thing is this, that among the lower animals 

 especially, but in all to some extent, there are processes 

 of rejuvenescence which counteract the processes of 

 senescence. In the single-celled animals the two bal- 

 ance ; in some simple creatures just mentioned they 

 also balance. Why should this not occur higher up 

 the scale ? The probable reason is this, that in a com- 

 plicated creature there has to be a more or less per- 



